A conventional swivelling device for a taphole gun comprises in an already known way a jib, the taphole gun being mounted on its free end. The other end of the jib is pivoted in a fixed supporting structure. The swivelling range of the jib should be as large as possible to enable the gun to swivel as far as possible from the runner. Furthermore, it should be stated that modern taphole guns operate with increasingly higher plugging pressures. Consequently the swivelling device, which is to press the plugging gun against the taphole, must also be designed for increasingly higher contact forces.
Hydraulic cylinders are currently used in the taphole plugging machines to swivel the jib. When work was still carried out with lower plugging pressures on the blast furnace, rotary motors were also used as the jib drive instead of the hydraulic cylinders. A taphole plugging machine with an electric motor is described, for example, in DE-A-895604. This electric motor transmits its force moment via a toothed-wheel and worm mechanism to the jib. A magnetic brake permits locking of the jib in the operating position. It is obvious that in the case of modern plugging machines with extremely high contact pressures such a solution is no longer economically viable.
A taphole gun with a hydraulic cylinder and hydraulic rotary motor is already known from U.S. Pat. No. 3,765,663. An arm securely connected to the jib, on which the piston rod of a double-acting hydraulic cylinder is secured by a first swivel joint, extends radially to the swivelling axis of the jib. The casing of this hydraulic cylinder is secured by a second swivel joint to a fixed arm, which projects a long way beyond the supporting structure of the jib. The hydraulic rotary motor is secured in the jib. It engages via a pinion with a gear wheel securely mounted on the supporting structure of the jib. This rotary motor swivels the jib between a rest and an operating position. The task of the hydraulic cylinder is merely to transmit a force moment to the jib in the operating position in order to press the gun against the taphole and subsequently pull it off again. The hydraulic cylinder is switched on only in a short swivelling range near the furnace. Its two pressure chambers are discharged to the tank over the remaining swivelling range. The stroke of the hydraulic cylinder is designed in such a way that during swivelling of the jib the length of the hydraulic cylinder is automatically adapted to the variable distance between the first and second swivel joints. In other words the swivelling device is a closed three-element mechanism, whereby the supporting structure forms the frame, the supporting arm the driven element, and the hydraulic cylinder, as an element with a variable length, closes the mechanism between the supporting structure and the jib.
A swivelling device for a taphole gun, which is intended to be characterised by its compactness, is already known from U.S. Pat. No. 4,247,088. It comprises a jib to carry the taphole gun, a supporting structure, in which the jib is pivoted at one end about a swivelling axis, a rotary drive to swivel the jib between its rest position and operating position and a hydraulic cylinder to generate a contact force. The hydraulic cylinder is supported by a lateral arm of the supporting structure. It is not securely connected to the jib, but can engage in a tooth system when the jib is swivelled into the operating position.